Automatic mercury monitor

ABSTRACT

APPARATUS AND METHOD ARE PROVIDED FORANALYZING GAS STREAMS FOR THEIR CONTENT OF IONIC, ELEMENTIC AND ORGANIC MERCURY EVEN IN THE PRESENCE OF OTHER CONTAMINATS, INCLUDING ELEMENTAL OR AVAILABLE CHLORINE OR ORGANIC MATTER. THE SAMPLE IS FIRST PYROLYZED AND THEN AUTOMICALLY MEASURED AND TREATED WITH AQUEOUS REDUCING REAGENT. THE RESULTING ELEMENTAL MERCURY IS TRANSFERRED TO A PHOTOMETRIC DETECTOR AND THE RESULTS ARE INDICATED AND/OR RECORDED AUTOMATICALLY, ACCURATELY AND RAPIDLY. THE APPARATUS AND METHOD ARE ESPECIALLY USEFUL IN THE CONTROL OF   MERCURY CONTAMINATION IN THE ENVIRONMENT AND ALSO FOR MONITORING CHEMICAL PROCESS STREAMS.

uly 3,, 1974 l. A. cAPuANo w3 fi AUT OMAT I C MERCURY MON I TOR Filed July 10, 1972 3 Sheets-Sheet l 5/ PYROLVZEF? SAMPLE I REAcE/vr STORAGE VACUUM our \ SAMPLE REAGENT VALVE VALVE PROGRAMMER DUTCTOR RECORDER INDICATOR f4/ July 30, 174

Filed July 10, 1972 l. A. CAPUANO AUTOMATIC MERCURY MONITOR 3 Sheets-Sheet 2 ZZZ United States Patent 3,826,618 AUTOMATIC MERCURY MONITOR Italo A. Capuano, Orange, Conn., assignor to Ionics, Incorporated, Watertown, Mass.

Continuation-impart of application Ser. No. 75,927, Sept.

28, 1970, now Patent No. 3,713,776, dated Jan. 30,

1973. This application July 10, 1972, Ser. No. 269,995

Int. Cl. G01n 21/24, 31/06 US. Cl. 23-232 R Claims ABSTRACT OF THE DISCLOSURE This application is a continuation-in-part of co-pending Ser. No. 75,927 filed Sept. '28, 1970, now US. Pat. 3,713,776, issued Jan. 30, 1973.

This invention relates to a method and apparatus for continuous, automatic analysis of a gas for its content of mercury. The mercury is suitably in the form of liquid mercury or vapor any other form reducible to metallic mercury by suitable aqueous reducing reagents. The fluid is suitably a flowing stream or discrete portions.

Aqueous liquids have previously been analyzed manually for mercury, reducing it to metal with stannous chloride, vaporizing the mercury and measuring photometrically the intensity of its 2537 Angstrom units spectral line. See Dill, US. Atomic Energy Commission, Report No. Y 1572, issued Mar. 28, 1967 and Rathje, American Industrial Hygiene Association Journal 30, 126-132 (1969).

The method and apparatus of this invention is useful for determining automatically the mercury content of air or other gases discharged to the atmosphere. Mercury contaminated gaseous streams originate in locations where mercury or its compounds are used in manufacturing various products, for example, in chlor-al kali plants operating mercury cells, felt manufacturing plants, plants for manufacturing mercury-containing pesticides, instruments, lamps, batteries and medicinals.

A major difficulty in controlling mercury contamination of the environment in industrial areas has been the lack of automatic apparatus capable of analyzing for mercury quickly, accurately and continuously. Some proposed methods and apparatus are not suited for ,use in contaminated environments where, for example, chloride gas adversely affects the function and structure of the apparatus or where other contaminants lead to false results. When mercury, as a contaminant, is present as the element or as salts, for example, as chloride salts, instruments employing pyrolytic reduction do not accurately respond to such mercury chloride salts. Because mercury is frequently present in various forms, gaseous samples cannot give accurate analyses when passed directly into many of the devices available for mercury analysis. This difficulty is overcome according to the present invention by converting the various forms of mercury to elementary mercury chemically and measuring its amount using instruments highly sensitive to the vapor or elementary mercury. The method and apparatus "Ice of the present invention is useful and accurate for analysis of samples containing other contaminants, particularly elemental or available chlorine.

The method and apparatus of this invention removes and measures a finite sample of the gas to be analyzed and processes the sample automatically to the finally indicated and/or recorded result. The sample is suitably removed and measured from a supply which may be moving or quiescent, i.e., it may be a flowing stream or a stationary body brought to the place of analysis. It is, however, a feature of the apparatus of the present inven tion, that it is portable and is suitably transported to the place where the gas to be analyzed is located. Advantageously, the sample points used in conjunction with the method and apparatus of this invention are located sufiiciently upstream of a disposal point to permit remedial steps to be taken to correct contamination before discharge of the stream under test when the method of this invention indicates the necessity of such action.

Mercury in the fluids analyzed is determined accurately and quickly by the method and apparatus of this invention when the mercury is present as one or more of the entities, Hg", Hg, Hg+ or organic mercury. Hg" represents elemental mercury, present as vapor or as droplets. The entity Hg+ represents monovalent ionic mercury usually present as suspended salts of mercurous mercury or as solids dispersed in a gas. The entity Hg' represents divalent ionic mercury usually present as suspended salts of mercuric mercury or as solids dispersed in a gas. These ionic forms of mercury are reduced and analyzed according to the method and in the apparatus of this invention.

The method and apparatus of this invention are also suita'bly used to measure the efiectiveness of operation of mercury-removing or mercury-introducing machines, processes and systems by measuring the mercury content of input and output streams.

The method of the present invention automatically monitors a gas for the total content of mercury when it is present therein as at least one of the entities, Hg", Hg and Hg+ or organic mercury by programming and mechanically performing successively and repetitively the operations of:

(a) providing aqueous reducing reagent in a reagent storage zone;

(b) removing from said reagent storage zone a reagent portion of predetermined amount and transferring said reagent portion to a scrubbing zonej (c) scrubbing said reagent portion in said scrubbing zone with a gaseous carrier;

(d) separating said gaseous carrier from the resulting aqueous liquid in said scrubbing zone;

(e) transferring said carrier to a measuring zone and automatically adjusting the base line reading to zero;

(f) providing a gas to be monitored for mercury present therein;

"g) transferring said gas to a pyrolyzing zone and pyrolyzing to remove interfering material;

(h) removing from the resulting pyrolyzed gas a sample of predetermined amount and transferring said sample to said scrubbing zone;

(i) scrubbing said sample in said scrubbing zone with said reagent;

(j) separating the resulting gases from the resulting aqueous liquid in said scrubbing zone;

(k) transferring said gases to said measuring zone and photometrically measuring the quantity of mercury in said gases;

(1) indicating the quantity of mercury in said gases relative to the predetermined amount of said sample.

1 (b) means for pyrolyzing a gas to be analyzed;

(c) means for removing from said gas a sample of predetermined amount and for transferring said sample to a scrubbing zone; 1

(d) means for circulating aqueous reducing reagent cyclically from a reagent storage zone through a reagent valve and through a reagent measuring zone and return to said reagent storage zone;

(e) means for removing from said circulating reagent a predetermined amount of said aqueous reagent and for transferring said amount of aqueou reagent to said scrubbing zone;

(f) means fol-scrubbing the mixture in said scrubbing zone with a gaseous carrier;

(g) means for separating said gaseous carrier containing mercury vapor from the resulting aqueous liquid in said scrubbing zone;

(h) means for transferring said carrier containing mercury vapor to a measuring zone;

(i) photometric means for measuring the quantity of mercury in said carrier;

(j) means for indicating the quantity of mercury in said carrier relative to the predetermined amount of said sample.

CALIBRATION Suitably, mercury-free gas and reference gases containing known amounts of mercury are introduced and analyzed in order to zero the detector and calibrate the system for gas analyses. Gases of known mercury content are used to zero the detector and calibrate the system for gas analyses. Care must be exercised to avoid the introduction of carrier gas containing unknown or variable amounts of mercury which would vititate the determination. Mercury-free carrier gas is suitably provided from a source of pure, compressed gas, advantageously, from a cylinder of compressed gas. Alternatively, air is suitably brought to the apparatus from a remote, uncontaminated plant location. The inert gaseous carrier is suitably air, nitrogen, hydrogen, helium, argon or other gases inert to the reducing reagent and non-absorbing in the ultraviolet region. The inert gases also containing minor amounts of contaminants, e.g., chlorine, are suitable.

The reducing reagent is an aqueous solution selected from the group consisting of aqueous stannous chloride and aqueous hydrazine. A suitable hydrazine reagent solution contains from 2 to 35 percent by weight of hydrazine with or without added alkali metal hydroxide in amounts of 1 to 10 percent. Suitable are any of the alkali metal hydroxides but sodium hydroxide is most common, cheapest and preferred. Preferred concentrations are about 10 percent of hydrazine and 5 percent of sodium hydroxide. When the sample gas contains chlorine, stannous chloride reagent is preferred.

Suitable aqueous stannous chloride reagent is a 5 percent solution of analytical grade SnCl -2H O in 1.2 N

hydrochloric acid. However, the composition of the aqueous reagent is not critical between 0.2 and 20 percent of stannous chloride in hydrochloric acid from 0.1 to N. Other suitable watersoluble stannous salts, for

example, stannous sulfate are also usable. The stannous chloride reagentis stable in the absence of air and is not significantly altered in the presence of air. A 50 ml. volume of aqueous reagent scrubbed at room temperature with 120 liters of air at'a rate of 2 liters per minute contained 2.00 percent and 1.90 percent of stannous tin before "and afterthc test. This simulates the air exposure of 'the 'r'eagent in the method and apparatus of this invention.

' At start-up,"a measured amount of aqueous reducing reagent is transferred to a suitable scrubber. Mercury-free 4 v carrier is bubbled through the liquid at a constant rate and is transferred to the detector. The detector is-then automatically zeroed by a servomechanism under the control of the programmer.

ANALYSIS OF GASES The gaseous sample suitably flows continuously at the same rate through the system as used in the calibration. The flow rate is maintained constant by vacuum and valve means and is suitably at about 2 liters per minute. However, the absolute valueof the flow rate is not critical between about 0.1 and 10 liters per minute using a reagent volume of preferably 50 ml. but suitably from 10 to ml.

The detector is zeroed using aqueous reducing reagent and mercury-free air.

A series of gas samples are analyzed and on completion of each series or at any other desirable interval, the liquid is discharged from the scrubber and replaced by a fresh, measured amount of aqueous reducing reagent to start a new cycle of analyses. 1

Elemental mercury present in the sample gas or formed in the scrubber by reduction of mercury compounds 'by the reducing reagent is vaporized in the gaseous stream and carried to the photometric detector which-comes to a steady analytical result as equilibrium is established: in the system. The final analytical result is suitably'recorded if desired. When gas samples contain high amounts of mercury, above the linear range of the detector, additional gaseous carrier is suitably introduced to dilute the sample to within the linear range of the detector.

A plurality of gaseous sample points are suitably selected serially by a programmer and the results recorded on a continuous chart. Each gaseous sample point is repeatedly sampled and analyzed at intervals determined by the number of such points multiplied by the time required for each analysis. Ordinarily, when shifting from one sample point to the next, about 3 minutes is required for equilibrium to be established in the system and an accurate analysis to be reported by the detector.

APPARATUS- The measurement and flow of sample, carrier gas and reagent are directed by any suitable programmer-operated valve having a suitable number of ports. One commercially available valve suitable for use as sample valve and reagent valve in the apparatus of this invention is the LG6 sliding insert valve No. W 122437 of Beckman Instruments Inc., but any other suitable valve will serve. Advantageously, such valves are fabricated of Kel-F or other suitable plastic parts and the ports and other fluid-carrying passages are lined with plastic. These valves suitably have a plurality of ports sufficient to perform the functions desired and may be from 2 to 10. The 6-port valves are suitable for sample and reagent valves in the apparatus of the present invention. Other valves in the system usually have 2 or 3 ports.

A terminal vacuum is generated and applied to induce the flow of fluids through the system. The vacuum generator is under control of the programmer and is activated when analyses 'begin and continues until analyses are completed. Suitably an exit pressure of 740:10 mm. is maintained when the inlet lines are at sea level atmospheric pressure. Alternatively, atmospheric pressure at the exit and superatmospheric pressure at the inlet aresuitable, maintaining differential pressures of about 10 to 30 mm.

DETECTOR One suitable detector is the Du Pont 400 photometric analyzer which is suitable for use with standard millivolt, self-balancing recorders having unbalanced impedance over 10,000 ohms. Analyzer output impedance is .up to 20,000 ohms. Power at volts and 60 hertz is supplied. A suitable recorder is Leeds and Northrup Speedomax H with a range of 0 to millivolts. Other suitable instruments are available.

The preferred detector has an ultraviolet light generator at one end which illuminates a one-meter tube through which carrier gas passes. Mercury vapor in the gas absorbs the 2537 Angstrom unit wave length and reduces the intensity of the light at the other end of the tube where a photocell is located. The current passing through the photocell is inversely proportional to the amount of mercury vapor in the tube.

PROGRAMMER Any suitable programmer is useful in the method and apparatus of this invention. Advantageously, the programmer incorporates selector means whereby any of a plurality of sample sources are activated to provide a sample for analysis according to the method of this invention. Suitably the programmer is a timer adapted to close and open circuits in sequence for selected periods of time, to activate and shut down the vacuum terminally applied to the system, to activate and shut down the aqueous reagent circulating pump, to open and close valves which permit the flow of measured amounts of reagent, sample and, when desired, inert diluent gas through the system and to activate and shut down the detector and recorder-indicator. Programmers are commercially available which are suitably adjustable to provide the desired sequence of operations. One suitable programmer is No. 520 manufactured by Beckman Instruments Inc. but other commercial devices are suitable.

DRAWINGS FIG. 1 illustrates a system of the invention capable of analyzing gaseous materials. FIG. 1 shows chemical flow lines but omits electrical lines shown in FIG. 2.

FIG. 2 shows the electrical system for controlling functions of the corresponding elements of FIG. 1 and omits the chemical flow lines.

FIG. 3 shows the electrical system for control of several gaseous sampling points.

FIGS. 1 and 2, lines 16, 16a and 16b are provided for introducing air and sample gas into the system through valves 48 and 49, operated by solenoids 50 and 51, respectively, under control of programmer 101 via lines 111 and 112 respectively. Sufiicient vacuum is applied via line 44 to draw the gases through the entire system. In analyzing a gas sample, the gas sample is introduced via line 12 into pyrolyzer 212, controlled by programmer 101 via line 312, thence via line 16a through valve 49 controlled by solenoid 51 to line 16 controlled by the pressure regulator consisting of valve 17 and line 18 and through valve 32 operated by programmer 101 using line 104 to solenoid 33. Sample valve 11 is activated by programmer 101 via line 102 to permit flow of the gas from line 16 through line 20-to scrubber 21.

Pump 24 normally circulates aqueous reagent from reagent storage 25 to reagent valve 22 via line 26, through measuring device 29 via lines 28 and 30 and back to reagent storage 25 via lines 23 and 27. Programmer 101 operates via line 108 to shut down pump 24 and reagent valve 22 is operated to withdraw air from line 31 into line 28. Flow of air in line 31 is regulated by valve 34 operated by solenoid 35 under control of programmer 101 via line 105. Air and the measured quantity of aqueous reagent is transferred via. line 36 to scrubber 21.

In scrubber 21, the aqueous reagent reacts to reduce mercury ions to metallic mercury. The gas is separated from the aqueous portion of the contents of scrubber 21 and transferred via line 37 to detector 38. This transfer is controlled by valve 39 operated by solenoid 40 programmed by programmer 101 via line 106. Detector 38 indicates the amount of mercury in the air carrier relative to the predetermined amount of original sample and advantageously records the result by means of connected recorder-indicator 41. Detector 38 operates on a flow of gas, which is exhausted via line 42 through flowmeter 43 under the influence of vacuum applied via line 44. The complete analysis from time of sampling to time of indicating the result requires about 6 minutes.

One charge of aqueous reagent to scrubber 21 suffices for automatic zeroing on a mercury-free gas stream and for a plurality of gas analyses after which the aqueous reagent is discharged. To do so, programmer 101 energizes solenoid 40 via line 106 and opens valve 39 to admit air via line 52 and also energizes solenoid 47 via line 107 and opens valve 46, whereby the used aqueous reagent is discharged via line 45.

FIG. 3 shows a suitable sampler adapted for providing samples for analysis. Four sample points, A, B, C and D, are shown, it being understood that any desired number of sample points are suitably provided. Lines 53, 54, 55 and 56 are provided for gaseous fluids as appropriate from sample points A, B, C and D respectively. Each line leads to a three-way valve, 57, 58, 59 and 60 which is turned, when the sample line is not in use for analysis, to flow the fluid via lines 61, 62, 63 and 64 respectively to flowmeters 65, 66, 67 and 68 respectively. The flowmeters serve to indicate that the fluid is flowing normally through unclogged lines and via line 69 to a vacuum discharge.

When programmer 101 automatically selects sample point A for analysis, valve 57 is turned by solenoid 70, actuated via line 113, to flow sample from line 53 through line 71 and 72 to analysis. When analysis of the sample is completed, valve 57 is returned to its previous position. Other sample points are similarly sampled.

Example I Air samples for analysis were prepared containing various concentrations of mercury vapor. Liquid mercury was vaporized by passing air at a measured rate over a mercury pool in a chamber maintained at 27 C. and the resulting air stream was diluted by measured amounts of mercury-free air to provide samples of containing known amounts of mercury vapor.

Serially, the various samples so-prepared were introduced into gas sample line 16a of a system corresponding to FIGS. 1 and 2 using stannous chloride as reducing reagent and the samples were serially analyzed. The data in Table I show that accurate mercury analyses were obtained.

Samples of chlorine cell room air were analyzed by the standard iodine monochloride (ICl) method and in the system of FIGS. 1 and 2 using stannous chloride as the reducing reagent. The data in Table II show that accurate mercury analyses were obtained (control measures then began).

TABLE II Comparison of iodine monochloride (1011) method versus mercury monitor on chlorine cell room air samples 101 methfid7 Moniiciiri mg. g mg. g

m. m air Difference Average mean deviation i=0. 0055 I Example III Air samples containing various 'ar'nounts'of mercury were prepared as described-in Example I. They were Table III.

TABLE III Recovery of mercury from air samples with hydrazine Mercury I added Found (mg/m (mg/m Sample number:

What is claimed is:

1. Method for automatically monitoring a gas for the total content of mercury by programming and mechanically performing successively and repetitively the operations of:

(a) providing aqueous reducing reagent in a reagent storage zone;

(b) removing from said reagent storage zone a reagent portion of predetermined amount and transferring said reagent portion to a scrubbing zone;

(0) scrubbing said reagent portion in said scrubbing zone with a gaseous carrier;

(d) separating said gaseous carrier from the resulting aqueous liquid in said scrubbing zone;

(e) transferring said carrier to a measuring zone and automatically adjusting the base line reading to zero;

(f) providing a gas to be monitored for mercury present therein;

(g) transferring said gas to a pyrolyzing zone and pyrolyzing to remove interfering material;

(h) removing from the resulting pyrolyzed gas a sample of predetermined amount and transferring said sample to said scrubbing zone;

(i) scrubbing said sample in said scrubbing zone with said reagent;

(j) separating the resulting gases from the resulting aqueous liquid in said scrubbing zone;

(k) transferring said gases to said measuring zone and photometrically measuring the quantity of mercury in said carrier;

(1) indicating the quantity of mercury in said carrier relative to the predetermined amount of said sample.

2. Method as claimed in claim 1 in which said reducing reagent is aqueous stannous salt.

3. Method as claimed in claim 1 in which said reducing reagent is an aqueous solution of hydrazine.

4. Method as claimed in claim 1 in which said gas is air.

5. Method as claimed in claim 1 in which the quantity of mercury vapor in said carrier is measured photometrically by radiating said mercury vapor with electromagnetic energy of wave length 2537 Angstrom units and ineaslnring the amount of the energy absorbed at said wave engt '1 6. Method as claimed in claim 1 in which the quantity of mercury relative to thc'pjredetermined amount of'said sample is additionally recorded.

' 7. Method as claimed in claim 1 in which a plurality of samples of diverse gases are each continuously treated until the resulting photometric measurement acquires 'a steady state and automatically switching'to a sample of another gas until the samples of the "total number-of gases are analyzed and then repeating the cycle.

8. Apparatus for monitoring a gas for the mercury content which comprises:

(a) programming means for mechanically'activating and deactivating successively and repetitively:

(b) means for pyrolyzing said gas to be analyzed;

(c) means for removing from said gas a sample of predetermined amount and for transferring said sample to a scrubbing zone;

(d) means for circulating aqueous reducing reagent cyclically from a' reagent storage zone through a reagent valve and through a reagent measuring zone and return to said reagent storage zone;

(e) means for removing from said circulating reageht a predetermined amount of said aqueous reagent and for transferring said amount of aqueous reagent "to said scrubbing zone;

(f) means for scrubbing the mixture in said scrubbing zone with a gaseous carrier;

(g) means for separating said gaseous carrier containing mercury vapor from the resulting aqueous liquid in said scrubbing zone;

(h) means for transferring said carrier containing mercury vapor to a measuring zone;

(i) photometric means for measuring the mercury in said carrier;

(j) means for indicating the quantity of mercury in said carrier relative to the predetermined amount of said sample.

9. The apparatus of claim 8 including means for admixing and proportioning gaseous carrier with said predetermined amount of aqueous reagent and for transferring the resulting mixture of said aqueous reagent and said carrier to said scrubbing zone.

10. The apparatus of claim 8 including means for recording the quantity of mercury in said'carrier relative to the predetermined amount of said sample.

quantity of References Cited Dill, M. S., Research and Development Report Rathje, A. 0., Amer. Indust. Hygiene Assoc. Journal,

vol. 30, pp. 126-132 (1969). 1

Hatch, R. et al., Anal. Chem., vol. 40, pp. 2085-87 RONALD E. SERWIN, Primary Examiner US. 01. X.R. 23-230 PC, 254 R,"255 R 

